Previously collected urine specimens from 100 patients referred to the UK National CJD Surveillance Unit as suspected cases of Creutzfeldt-Jakob disease (CJD) were analyzed, testing for abnormal prion protein (PrPSc). In this context, the test had a low sensitivity and was not completely specific for CJD. Additionally, the proteins detected by this assay were not PrPSc but appeared to be immunoglobulins.